High-pressure synthesized trigonal CoxTi2S4: An intercalated sulfide with intermediate Co valence

The intercalation of magnetic ions into layered sulfides provides a flexible route to low-dimensional magnetism and spin-orbit-coupled phenomena. We report the high-pressure synthesis of the cobalt intercalated sulfide Co ₓ Ti 2 S 4 and discuss its structure, electronic, and magnetic properties. Synchrotron X-ray diffraction and Rietveld refinement reveal a trigonal structure (space-group: ̅ P 3 ̅ m 1 , No. 164) with lattice parameters a = 3.4041(6) Å, c = 5.6249(6) Å. The structure consists of alternating [CoS 6 ] and [TiS 6 ] layers along c -axes, analogous to the parent TiS 2 framework. XAS analyses reveal significant local structural disorder around the Ti sublattice, which is consistent with multiple Ti electronic configurations potentially associated with mixed Ti 3+ /Ti 4+ character. The main Co K-edge XANES features are reproduced by a Co-centered cluster encompassing the first two coordination shells. Compositional analysis reveals a polycrystalline, heterogeneous microstructure, consistent with partial intercalation and a refined composition of Co 0.8 Ti 2 S 4 . Magnetic measurements show a large temperature-independent magnetic contribution together with a weak Curie contribution from a small fraction of Co 2+ ions within a predominantly non-magnetic Co 3+ matrix, giving an effective moment of ≈ 0.26 μ B /f.u. The absence of long-range order down to ~1.8 K, together with weak FC/ZFC irreversibility and sigmoidal M ( H ) isotherms, is consistent with a minority contribution from Co-rich magnetic regions exhibiting cluster-like or superparamagnetic-like behavior, in contrast to the cluster-glass behavior of Ni 0.8 Ti 2 S 4 and the long-range order in Fe ₓ Ti 2 S 4 . This work establishes Co 0.8 Ti 2 S 4 as a tunable platform for exploring the interplay between Co intercalation, local structural disorder, and magnetic behavior in layered transition-metal sulfides.